When embroidering on a textile material it is desirable that the embroidery area of the textile material is kept as crease-free and as tensioned as possible in order to make the embroidery work as easy as possible. An embroidery frame is often used for tensioning and keeping the textile material in place. Traditionally, embroidery has been performed manually using embroidery frames of circular shape, which usually comprise one frame with a fix diameter and one frame with an adjustable circumference. The textile material intended for embroidering is clamped between the inner and the outer frames through adjusting the circumference of the outer frame by means of some type of mechanism such that the frames are pressed together. An interlining, of, for example, Vliseline, is usually placed as support under the textile material intended for embroidering. The interlining is clamped in the embroidery frame together with the textile material and is thus sewed on to the textile material when embroidering is performed. After embroidering is finished, the interlining is removed through, for example, tearing away.
Today, there are sewing machines with an embroidery function on the market, which are often provided with a separate embroidery unit for embroidering on a textile material. Such an embroidery unit is typically mounted onto the sewing machine as an extra unit and one embroidery frame with a clamped and tensioned textile material is attached to the embroidery unit. The embroidery frame may be moved around by means of the embroidery unit in a pre-programmed path such that stitches forming an embroidered pattern are placed on the clamped and tensioned textile material by the sewing machine. The development of sewing machines with an embroidery function implied that the need for embroidery frames having a rectangular shape increased, since rectangular embroidery frames utilize the rectangular working area of the sewing machine in a better way. In use of a rectangular embroidery frame based on the same principle as the above mentioned circular embroidery frame, the clamping force on the textile material will however be unequally distributed. A considerably greater clamping force is then obtained at the corners than at the sides, where the clamping force will be small. The manufacturers have tried to remedy the problem with keeping the textile material sufficiently clamped even at the sides by using, for example, clips that keep the inner and outer frames together, different types of interlinings and various profiles of the inner and outer frames. Another problem with many of the embroidery frames on the market today is that they require that a high force is applied manually, since the tensioning of the textile material is performed totally manually.
A well functioning embroidery frame should, among other things, typically imply an easy mounting and loosening of one textile material, that the textile material is strongly kept in place, that the textile material does not move during embroidering, that no marks are left on the textile material as well as that as many qualities of the textile material and as many different values of the thickness of the textile material as possible are possible to utilize. The length and the width of the embroidery frame are restricted by the size of the embroidery unit. Furthermore, the dimensions of the cross-section of one embroidery frame for one sewing machine are typically determined by the position of the foot and the size of the worktable.
It is previously known to provide a device, for example an embroidery frame, with a member that can be filled with a gas or a liquid and that tensions and clamps a material by increasing its diameter upon filling. An embroidery frame for industrial use is known from U.S. Pat. No. 5,129,171, which comprises a rigid component, a tensioning component and a tensioning tube. Material intended for embroidering is placed on the upper surface of the rigid component and the tensioning component is placed on the upper side of the material for initial clamping of the textile. The tensioning tube expands upon filling with a gas or a liquid and operates in a flute formed between the tensioning component and the rigid component. When the circumference of the tube is increased, the flute is initially expanded, which facilitates the movement for tensioning of the textile, and is finally narrowed, which implies that a strong clamping force is obtained at the end of the tensioning movement. Furthermore, the tensioning tube is crease-free with a bias-belted body comprising two layers of parallel strength-ensuring members, which imply that the textile depending on the angle they enclose with respect to a circumferential direction can be tensioned by increasing or decreasing the pressure alternatively, i.e. increasing or decreasing the circumferential length alternatively.
One disadvantage with the device in accordance with U.S. Pat. No. 5,129,171 is that a strong clamping of the textile is not achieved before after the tensioning of the textile. Furthermore, a relatively high pressure is required in one tube in accordance with U.S. Pat. No. 5,129,171 in order to by means of pressurization achieve expansion of the tube by increasing its diameter, i.e. stretching of the tube. A high pressure in the tube as well as the fact that the tube is to be stretched make great demands on the strength of the tube and on the inner and outer frames too, which are affected by the tube. The cost of production of such a tube, inner frame and outer frame will thereby be high.